The present invention relates to vehicle air conditioners and displacement control valves for controlling displacement of variable displacement compressors used in the air conditioners.
A typical refrigerant circuit in a vehicle air-conditioner includes a condenser, an expansion valve, an evaporator and a compressor. The compressor is driven by a vehicle engine. The compressor draws refrigerant gas from the evaporator, then, compresses the gas and discharges the compressed gas to the condenser. The evaporator performs heat exchange between the refrigerant in the refrigerant circuit and the air in the passenger compartment. The heat of air at the evaporator is transmitted to the refrigerant flowing through the evaporator in accordance with the thermal load or the cooling load. Therefore, the pressure of refrigerant gas at the outlet of or the downstream portion of the evaporator represents the cooling load.
Variable displacement compressors are widely used in vehicles. Such compressors include a displacement control valve that operates to maintain the pressure at the outlet of the evaporator, or the suction pressure, at a predetermined target level (target suction pressure). The control valve feedback controls the displacement of the compressor by referring to the suction pressure such that the flow rate of refrigerant in the refrigerant circuit corresponds to the cooling load.
The displacement control valve includes a pressure sensitive member that moves the valve body in accordance with the suction pressure. The pressure in the crank chamber is adjusted in relation to the position of the valve body. The inclination angle of a swash plate located in the compressor is altered depending on the pressure in the crank chamber. This varies the displacement of the compressor.
A certain type of displacement control valve alters the target suction pressure through an external electric control procedure. The control valve includes an electromagnetic actuator such as a solenoid. When an electric current is externally supplied to the electromagnetic actuator, the actuator urges the pressure sensitive member with the force varied in relation to a value of the electric current. The value of the electric current reflects the target suction pressure.
However, the actual suction pressure reaches the target value, which is changed through the electric control procedure, only after a certain delay. More specifically, the thermal load that acts on the evaporator affects the suction pressure, thus causing the delay. Accordingly, although the target suction pressure is adjusted accurately through the electric control procedure, the displacement of the compressor cannot be varied quickly or smoothly.
It is an objective of the present invention to provide an air conditioner and a displacement control valve of a variable displacement compressor that vary compressor displacement quickly and smoothly.
To achieve the above objective, the present invention provides an air conditioning apparatus provided with a refrigerant circuit including a variable displacement compressor. The air conditioning apparatus includes a displacement control mechanism, which controls the displacement of the compressor in relation to a pressure difference between a first pressure monitoring point and a second pressure monitoring point in the refrigerant circuit such that the pressure difference seeks a predetermined target value. The second pressure monitoring point is located downstream of the first pressure monitoring point. The displacement control mechanism has an altering device for altering the target value. A first pressure introducing passage introduces the pressure at the first pressure monitoring point to the displacement control mechanism. The first pressure monitoring point and the first pressure introducing passage form a high pressure zone. A second pressure introducing passage introduces the pressure at the second pressure monitoring point to the displacement control mechanism. The second pressure monitoring point and the second pressure introducing passage form a low pressure zone. An adjusting line connects, the high pressure zone to the low pressure zone. An adjusting valve adjusts the opening size of the adjusting line.
The present invention also provides a displacement control valve for controlling the displacement of a variable displacement compressor incorporated in a refrigerant circuit of an air conditioning apparatus. The control valve includes a valve housing, a valve body, which is accommodated in the valve housing, a pressure sensitive chamber, which is formed in the valve housing, and a pressure sensitive member, which divides the pressure sensitive chamber to a first pressure chamber and a second pressure chamber. The pressure at a first pressure monitoring point in the refrigerant circuit is introduced to the first pressure chamber. The pressure at a second pressure monitoring point in the refrigerant circuit is introduced to the second pressure chamber. The pressure sensitive member moves the valve body in accordance with the pressure difference between the first pressure chamber and the second pressure chamber, thereby controlling the displacement of the compressor such that the pressure difference between the first and second pressure monitoring points seeks a predetermined target value. The control valve further includes an altering device for altering the target value. The altering device urges the valve body with a force corresponding to the target value. An adjusting line is formed in the pressure sensitive member to connect the first pressure chamber to the second pressure chamber. An adjusting valve adjusts the opening size of the adjusting line.